Re: [Qemu-devel] [qemu-s390x] [PATCH v3 1/7] s390x/pci: factor out endianess conversion

[Cornelia Huck]

On Mon, 27 Nov 2017 16:24:08 +0100
Pierre Morel <address@hidden> wrote:

> On 27/11/2017 15:34, Cornelia Huck wrote:
> > On Mon, 27 Nov 2017 12:02:55 +0100
> > Cornelia Huck <address@hidden> wrote:
> >   
> >> On Mon, 27 Nov 2017 07:59:36 +0100
> >> Thomas Huth <address@hidden> wrote:
> >>  
> >>> On 25.11.2017 14:49, Pierre Morel wrote:  
> >>>> On 24/11/2017 07:19, Yi Min Zhao wrote:  
> >>>>>
> >>>>>
> >>>>> 在 2017/11/23 下午8:18, Thomas Huth 写道:  
> >>>>>> On 23.11.2017 13:07, Yi Min Zhao wrote:  
> >>  
> >>>>>>> Another question, does 'cpu' in cpu_to_le**() or le**_to_cpu() mean 
> >>>>>>> the
> >>>>>>> host endianess?  
> >>>>>> Yes, the "cpu" in cpu_to_le or le_to_cpu means the host, indeed. It's
> >>>>>> confusing :-/
> >>>>>>       
> >>>>>>> If the answers to upper two questions are yes, we actually need handle
> >>>>>>> two cases.
> >>>>>>> 1) For pcilg, we need to translate the data to little-endian, thus
> >>>>>>> cpu_to_le**().
> >>>>>>> 2) For pcistg, we need to translate the data to host endianess, thus
> >>>>>>> le**_to_cpu().  
> >>>>>> I think we've got to byte-swap if the host is big endian (s390x), but
> >>>>>> not if the host is little endian (x86 with TCG).  
> >>>>
> >>>> Here is my comprehension of this funny swapping:
> >>>>
> >>>> - TCG for a BE guest and a le host swap bytes because if we do (register
> >>>> & 0x01) in the zPCI interception code it must work what ever the
> >>>> endianess is.  
> >>>
> >>> Uhhh, I might have missed that the value has already been byte-swapped
> >>> once by TCG for env->regs[r1] ...
> >>> Now I'm pretty much completely confused ... sorry for the noise if I was
> >>> wrong... I think it's best you ignore my comment for now (i.e. go with
> >>> bswapXX() instead of le_to_cpuXX()), and if we later wire up zPCI with
> >>> TCG, we still can fix this if necessary.  
> >>
> >> I'll try my current pci/tcg patches on LPAR with this (or a v4) on top.
> >> If it works there (it doesn't yet on my laptop), we do have a
> >> endianness issue... (unfortunately, the reverse isn't true.)  
> > 
> > It does not look too bad: I can get a nice enP1p0s0 device from a
> > virtio-net-pci with my tcg patches on my laptop (with these patches as
> > well, of course). So, endianness is likely mostly fine.  
> 
> On the Lpar and on the Laptop or only on the Lpar ?

Both :)

> 
> >   
> >>
> >> I'll post my pci/tcg patches once I get it mostly working (and it does
> >> not look like a horror from the crypt anymore).  
> > 
> > Time to get out the make up kit for these.
> >   
> 
> 
>